Depending on environmental conditions such that a hydraulic working machine is installed in an upland area or performs work in an environment of extremely low temperatures or use conditions of a hydraulic working machine such that work is performed using inferior fuel or different work loads are applied to the hydraulic working machine, a prime mover, that is, an engine may be overloaded even if the hydraulic machine is the same. In such a case, a need arises to limit the engine output. It is, hence, necessary for a maintenance service engineer to visit the site and to adjust the maximum absorption torque of the main pump of the hydraulic working machine. This adjustment of the maximum absorption torque of the main pump requires special equipment such as service tools, and moreover, the maintenance service engineer is required to have good skills and experiences.
In addition to a main pump, sub-pumps different in the manner of control and the manner of use from the main pump, such as a cooling fan pump and a pilot pump, are also connected to an engine. In other words, plural pumps different in characteristics from each other are connected to an engine. Unless the above-mentioned adjustment is performed well, an interference takes place in pump absorption torque among the pumps to adversely affect the operability and working performance of the hydraulic working machine.
Conventional technologies of the above-mentioned sort include those disclosed in Patent Documents 1 and 2. The conventional technology disclosed in Patent Document 1 is to change the setting of the engine revolution speed depending on the altitude. The conventional technology disclosed in Patent Document 2, on the other hand, is to use a sealed bellows vessel, which can expand or contract depending on the atmospheric pressure to make the absorption torque of a pump variable in accordance with the atmospheric pressure.
Patent Document 1: JP-A-2004-132197
Patent Document 2: JP-A-9-126150